How to use an exported Cycles image as a projected image in Unity?
Render your view to an image Rendered.png
Go to UV Editing
Set the right pane (3D View) to camera view (Num .)
Select Rendered.png on the image viewer on the left
Choose one of your objects
Enter Edit Mode (Tab)
Select All (A)
Press U and choose Project From View
Repeat steps 4-7 for all other visible objects
Go back to Default workspace
Open a node editor
Set up the nodes as shown



I don't know if Window Projection actually exports to Unity but I suppose there is an equivalent setting there. Actually the small cube does not need such a Texture Coordinate, and frankly I don't understand why the outer shell needs it, I was expecting it to work out of the box.